Two new studies find that weight-loss surgery is significantly more effective than standard treatments for controlling blood sugar in overweight and obese people with Type 2 diabetes.

Although research has previously hinted that bariatric surgery, which shrinks the stomach and reroutes food to the intestines, can reverse diabetes — sometimes even before patients leave the hospital — the two new studies published Monday in the New England Journal of Medicine are the first randomized trials to pit surgery against standard treatments head-to-head.

Compared with patients getting blood-sugar-controlling medication and counseling in diet and exercise, those who received bariatric surgery were far more likely to be free of diabetes or to have reduced their dependence on diabetes medications for at least two years, compared with those not getting the surgery.

By closing off most of the stomach to food, people who receive bariatric surgery eat less and, therefore, lose weight. Patients in the studies lost about five times as much weight on average as those only taking blood-sugar-lowering medications. Weight gain is key a risk factor for Type 2 diabetes, and losing excess weight can help many patients control their disease. But doctors also believe that weight-loss surgery itself, independent of weight loss, can help manage diabetes. Eating too many calories can overwhelm the body’s insulin-producing abilities and lead to higher levels of unprocessed sugar in the blood, so stomach-shrinking surgery may benefit patients by helping them consume less.

“Bariatric surgery should not be considered just weight-loss surgery,” Dr. Francesco Rubino of Weill Medical College of Cornell University and author of one of the studies, told ABC News, “but a means to treat diabetes and metabolic disease.”

In one study, led by Rubino and his colleagues at the Catholic University in Rome, 75% of the patients who had bariatric surgery no longer had diabetes after two years, compared with zero patients who relied on drug treatments alone.

In the second trial, led by researchers at the Cleveland Clinic, 37% to 42% of patients having the surgery and using diabetes medications were able to keep their blood glucose levels below the threshold doctors use to diagnose diabetes, compared with 12% of those who depended only on the medications, after a year.

“The result is simply stunning,” Dr. Steven Nissen, chairman of cardiovascular medicine at the Cleveland Clinic and an author of the paper, toldUSA Today.

Still, Nissen and other experts aren’t ready to go so far as to declare bariatric surgery a cure for diabetes. While weight gain is a major contributor to the disease, other risk factors, including a family history and genetic predisposition, also play important roles, which surgery may not fully address.

There is also the complex interaction between diabetes medications and weight; in a cruel metabolic twist, some of the drugs designed to control glucose levels can also cause weight gain. That may be why earlier studies of bariatric surgery have suggested that the procedure may not work for everyone. In one trial from 2008, researchers found that diabetes patients undergoing gastric bypass did not lose as much weight after a year as did those who did not have diabetes to begin with; 92% of those without diabetes were able to lose 40% or more of their weight after 12 months, which constituted a successful operation, compared with only 79% of those with diabetes.

Still, the current results provide reason to investigate the role that bariatric surgery may play in helping at least some diabetic patients to control, and perhaps even overcome, their disease. Not everyone will be an ideal candidate for surgery nor will many patients have the financial means to take advantage of the procedure, but the findings hint that hormones that normally control appetite, which may be suppressed with weight gain, could be re-engaged when excess weight comes off and help to normalize the body’s insulin and glucose levels.